Cool storage type air conditioners are now put into practical use in which refrigerators are operated in the nighttime for the purpose of leveling daytime and nighttime loads.
Although chilled water has been commonly used as a cool storage medium, attention has recently been directed to the use of ice. This is because, when the latent heat of fusion (80 Kcal/kg) of ice is utilized, the volume of a cool storage apparatus can be greatly decreased (usually less than 1/5 of the volume required hitherto).
However, a conventional ice maker heat pump which requires a heat-exchange bank (such as an ice maker coil) for heat exchange between a cooling medium (such as a refrigerant or an antifreezing solution) and water has had the following defects among others:
1. The evaporation temperature of the refrigerant in the refrigerator is low (-6.degree. C. to -18.degree. C.), and the operation efficiency (the coefficient of performance) is low.
2. The ice maker heat exchanger is bulky, resulting in a high cost.
To solve such problems, an ice making process of direct contact type (as, for example, disclosed in U.S. Pat. No. 3,838,577) has been proposed in which a refrigerant insoluble to water (a Freon or a hydrocarbon in most cases) is introduced into water and flashed into vapor to form ice crystals in the water. In conjunction with a process of turning sea water into fresh water (by freezing), crystallization was practically tested (4th International Symposium on Fresh Water from the Sea, Vol. 3, 371-382, 1973).
Applications of ice maker heat pumps to air conditioners were also proposed (Residential 182-187, A NEW CONCEPT FOR THE ICE MAKER HEAT PUMP), and development for practical use has also been attempted.
A heat exchange process of direct contact type similar to that described above uses cool storage by a clathrate (which is an inclusion compound of water and is also called a gas hydrate) in lieu of ice (Chemical Engineering, August 1982, pp. 31-36).
However, none of applications of the ice maker heat pumps to air conditioners have been successfully put into practical use.
The reasons are as follows:
(i) In the case of ice storage according to a heat exchange process of direct contact type proposed or attempted hitherto, a crystallizer and an ice bank have been separately provided, and ice slurry produced in the crystallizer has had to be continuously transferred to a storage tank (Residential 182-187). In this system, however, fine droplets of the portion of the refrigerant which has not been vaporized migrate toward the ice bank together with the ice crystals. Therefore, the prior art system has been defective in that the quantity of the refrigerant (R114, C318, or the like) constituting the refrigeration cycle becomes insufficient to continue the operation. Further, the prior art system has also been defective in that requirements of two tanks, ice slurry piping, ice slurry pumps, etc. lead to a complicated structure. PA1 (ii) In the case of clathrate storage, a refrigerant is taken into crystal lattices of water molecules when a clathrate is formed. Therefore, the quantity of the enclosed refrigerant (R12 or the like) is very large (about 1/3 of that of water) and amounts to the order of tons even in a building of small scale. PA1 (a) The refrigerant acts only as a working fluid for a refrigeration cycle, and its quantity to be charged is small (almost equal to that required in a common refrigerator). PA1 (b) The heat transferability is satisfactory since ice is made by direct contact heat exchange. Therefore, the refrigerant can be vaporized at a temperature (-2.degree. C. to -1.degree. C.) lower than the freezing temperature of water, and the coefficient of performance can be improved. PA1 (c) Chilled water (whose temperature is preferably 5.degree. C. to 7.degree. C.) to be supplied to an air conditioner is cooled by a heat exchanger provided in a tank. (The heat exchanger may be provided outside of the tank.) Since the temperature of ice is 0.degree. C., there is a sufficient temperature difference for heat exchange. PA1 (d) The tank is gastight, and no oxygen gas is substantially present in the tank. Therefore, no rust occurs even when the tank is made of an inexpensive steel material.
Thus, there are still many problems to be solved from the aspects of cost and safety.
Further, a refrigerant which forms a clathrate has generally a small molecular weight and a high vapor pressure (6.6 kgf/cm.sup.2 absolute at 25.degree. C. in the case of R12). Therefore, a refrigerant container capable of withstanding a high pressure is required, resulting in a high equipment cost.
Based on an experiment of clathrates and also on the above consideration, the inventor proposed a new ice maker heat pump in Third Annual Workshop on Ice Storage for Cooling held at Argonne National Laboratory on Nov. 21-22, 1983, sponsored by the Department of Energy of U.S.A. In this proposal, a refrigerant having a large molecular size (more than 7 .ANG., R114 herein) is selected so as not to form a clathrate, although the structure of the heat pump is similar to that of the clathrate-forming heat pump.
Intended advantages of the proposed system are as follows:
In contrast, the clathrate has a high melting point (which is between 4.degree. C. and 12.degree. C. and which differs depending on the refrigerant). Therefore, the clathrate is suitable to provide a sufficient temperature difference for heat exchange.
However, later researches and studies have proved that the liability of Freons (halogeno-hydrocarbons) to hydrolysis is a vital defect. That is, hydrolysis of halogeno-hydrocarbons produces reaction products such as hydrogen chloride (hydrochloric acid), hydrogen fluoride (hydrofluoric acid), etc., and the presence of even a very slight quantity of such reaction products gives rise to danger of corroding the tank, compressor, heat exchanger, etc. Further, even when the rate of hydrolysis is very slow, the adverse effect of accumulation of such reaction products during a long time of use (more than 10 years) of the system in a closed state cannot be ignored.
Based on the finding described above, the present invention contemplates to provide an improved ice storage refrigerating apparatus of direct contact type.
A primary object of the present invention is to provide an ice storage refrigerating apparatus of direct contact type comprising a closed crystallizer tank containing water therein, and a refrigerant system including means for cooling to condense a refrigerant of gas form consisting essentially of a hydrocarbon having four carbon atoms and/or a hydrocarbon having five carbon atoms, means for bringing the condensed refrigerant gas into direct contact with the water to form ice in sherbet form, and means for circulating the refrigerant gas from the top of the crystallizer tank to recover the refrigerant.
Another object of the present invention is to provide the ice storage refrigerating apparatus of direct contact type described above, wherein the refrigerant system includes nozzle means disposed in a lower part of the crystallizer tank for ejecting the condensed refrigerant gas into the water contained in the crystallizer tank.
Still another object of the present invention is to provide an ice storage refrigerating apparatus of direct contact type comprising a closed crystallizer tank containing water therein, and a device for directly ejecting a refrigerant consisting essentially of a hydrocarbon having four carbon atoms and/or a hydrocarbon having five carbon atoms into the water contained in the crystallizer tank thereby forming ice in sherbet form, the device comprising pipe means having an open upper end located adjacent to the water level in the crystallizer tank and an open lower end located in a lower part of the crystallizer tank, and nozzle means extenting into the pipe means for ejecting the refrigerant therefrom.
Yet another object of the present invention is to provide an ice storage refrigerating apparatus of direct contact type comprising a gastight crystallizer tank enclosing therein water and a refrigerant substantially insoluble to the water, a condenser disposed in an upper space of the crystallizer tank and cooled by an external refrigerator for condensing the refrigerant, and sprinkler means disposed in the upper space for sprinkling the liquid pumped out from the bottom part of the crystallizer tank and fed through conduit means, the refrigerant dropping in liquid form from the condenser and the liquid pumped out from the bottom part of the crystallizer tank being mixed together on the liquid level in the crystallizer tank to form ice in particle form.
The peculiar character of the present invention, as well as other objects, features and advantages of the present invention, will become apparent from the following detailed description taken in conjunction with the accompanying drawings.